In brief, these results show that the dancer, under
the conditions of the experiments, is not able to
tell green from blue, or violet from red. The
evidence of discrimination furnished by the light blue-orange
tests is not satisfactory because the conditions of
the experiment did not permit the use of a sufficiently
wide range of brightnesses. It is obvious, therefore,
that a method of experimentation should be devised
in which the experimenter can more fully control the
brightness of the colors which he is using. I
shall now describe a method in which this was possible.
THE SENSE OF SIGHT: COLOR VISION (Continued)
There are three well-known ways in which colors may
be used as stimuli in experiments on animals:
by the use of colored papers (reflected light); by
the use of a prism (the spectrum which is obtained
may be used as directly transmitted or as reflected
light); and by the use of light filters (transmitted
light). In the experiments on the color vision
of the dancer which have thus far been described only
the first of these three methods has been employed.
Its advantages are that it enables the experimenter
to work in a sunlit room, with relatively simple,
cheap, and easily manipulated apparatus. Its
chief disadvantages are that the brightness of the
light can neither be regulated nor measured with ease
and accuracy. The use of the second method, which
in many respects is the most desirable of the three,
is impracticable for experiments which require as large
an illuminated region as do those with the mouse;
I was therefore limited to the employment of light
filters in my further tests of color discrimination.
The form of filter which is most conveniently handled
is the colored glass, but unfortunately few glasses
which are monochromatic are manufactured. Almost
all of our so-called colored glasses transmit the
light of two or more regions of the spectrum.
After making spectroscopic examinations of all the
colored glasses which were available, I decided that
only the ruby glass could be satisfactorily used in
my experiments. With this it was possible to
get a pure red. Each of the other colors was
obtained by means of a filter, which consisted of a
glass box filled with a chemical solution which transmitted
light of a certain wave length.
For the tests with transmitted light the apparatus
of Figures 20 and 21 was constructed. It consisted
of a reaction-box essentially the same as that used
in the brightness vision tests, except that holes were
cut in the ends of the electric-boxes, at the positions
G and R of Figure 20, to permit the light to
enter the boxes. Beyond the reaction-box was a
long light-box which was divided lengthwise into two
compartments by a partition in the middle. A
slit in the cover of each of these compartments carried
an incandescent lamp L (Figure 20). Between
